Reduction of tailpipe emissions may be a shared goal among manufacturers in the automotive industry. As the standards for emissions continue to increase, technologies may continually improve to meet the standards. Tailpipe emissions based on current standards may need to be reduced to meet future regulations. Previous approaches to reducing cold-start emissions include developing catalysts that can warm up quickly and light-off at lower temperatures and optimizing engine cold start conditions to deliver heat to the catalyst as quickly as possible. However, even with fast catalyst light-off, there is still a duration of time during a cold start when the catalyst is not warm enough to convert emissions species.
Some approaches utilize electric heaters to directly heat the catalyst. However, these approaches may demand additional energy storage devices arranged on-board a vehicle. Additionally or alternatively, such systems demand additional electrical connections between the electric heater and the energy storage device which may be difficult to route due to complex packaging of the engine. The electric heater and its wiring may be prone to degradation due to the high temperature environment about which they are arranged.
In other approaches, a backpressure valve may be introduced to the exhaust passage. The backpressure valve may increase backpressure during the cold-start. For example, U.S. Pat. No. 9,624,855 by Leone et al. teaches a backpressure valve arranged downstream of a catalyst. The valve may be activated during a cold-start to increase exhaust backpressure, which may allow the catalyst to reach a light-off temperature before emissions are released to an atmosphere.
However, the inventors herein have recognized potential issues with such systems. As one example, the valve increases packaging restraints and may be difficult to install due to the compact packaging of modern engine systems. Furthermore, the valve may provide no other function other than increasing exhaust backpressure. Lastly, the backpressure vale also demands its own wiring and connections to a controller and energy storage systems of the vehicle.
In one example, the issues described above may be addressed by a method comprising determining an engine cold-start and rotating a turbine of an electric turbocharger in a reverse direction to increase exhaust backpressure, the turbine being mechanically coupled to a compressor via a shaft. In this way, the turbine and the compressor are spun in reverse directions such that exhaust backpressure increases and intake manifold vacuum increases.
As one example, increasing intake manifold vacuum may allow vacuum of one or more vacuum consumption devices to increase. By synergistically utilizing the reverse spinning of the turbine to also reverse spin the compressor, vacuum may be replenished as the catalyst is warmed-up via the increased exhaust backpressure. Additionally, the turbine and compressor may be utilized to adjust intake pressures during engine operating conditions outside of a cold-start. For example, if manifold absolute pressure (MAP) increases to a MAP greater than an upper limit of a desired range, then the turbine, and therefore the compressor, may be spun in reverse to decrease MAP. This may increase exhaust backpressure, however, a rotational speed of the turbine is adjusted such that the exhaust backpressure may be tolerated during engine operating conditions outside of the cold-start such that combustion stability is not adversely effected.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.